Decouple module callback mechanism from CatalystInstance

Summary:
Create a JSInstance superinterface which doesn't include all
the lifecycle stuff.

Reviewed By: AaaChiuuu

Differential Revision: D4614410

fbshipit-source-id: 16047bbcb1bb69bf36a0a13ef68f3a6aa396a991

ReactAndroid/src/main/java/com/facebook/react/bridge/JSInstance.java

@@ -0,0 +1,24 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.react.bridge;
+
+/**
+ * This interface includes the methods needed to use a running JS
+ * instance, without specifying any of the bridge-specific
+ * initialization or lifecycle management.
+ */
+public interface JSInstance {
+  void invokeCallback(
+      ExecutorToken executorToken,
+      int callbackID,
+      NativeArray arguments);
+  // TODO if this interface survives refactoring, think about adding
+  // callFunction.
+}